Patent GB-885478-A (GB)
Title: Apparatus adapted to check the constancy of the throughput of textile material passing through it
IPC: G01N27/22
Filed: 1959-09-28
Abstract: 885,478. Determining physical dimensions. BUTTICAZ, A., and DEMBOWSKI, H. Sept. 28, 1959 [Sept.30, 1958; Dec. 20,1958], No. 32921/59. Class 37. [Also in Groups XXXVIII and XL (c)] Apparatus for detecing irregularities in continuously moving textile material 9 comprises a measuring head 1 connected through a flexible cable 2 with the main body 3 of the apparatus, the measuring head comprising a double capacitor having two lateral electrodes 4, 6 arranged symmetrically on either side of a central electrode 5 with means for guiding the textile material through the slot between the central electrode and one of the lateral electrodes, and the main body of the apparatus comprising indicator means and an oscillator having an output arranged symmetrically with respect to earth and connected through a screened twin line within the flexible cable 2 to the lateral electrodes 4, 6 of the capacitor, the central electrode 5 being connected through a coaxial line within the flexible cable 2 to the input of an amplifier within the main body 3 of the apparatus and supplying an output to actuate said indicating means. As shown in Fig. 9, the output of oscillator 61 is balanced with respect to earth by means of potentiometer 68 and applied to the lateral electrodes 4, 6 over line 47. The signal developed on central electrode 5, which varies with the thickness of the material passing between electrodes 5 and 6, is applied over conductor 48 to the input of an amplifier 71 tuned to the oscillator frequency. The output of the amplifier is rectified by means of diodes 79 and the varying unidirectional voltage developed across capacitor 80 is applied through non-linear resistor 83, resistor 82 and capacitor 80<SP>1</SP> to a meter 86, which in the absence of any input to capacitor 80 is biased to a mid-point on its scale by means of potentiometer network 85, 90. The potential developed at point C which is representative of the rectified output of amplifier 71 is applied through a filter network 91 to the control grid of the first valve of the amplifier 71 as an A.G.C. voltage. This causes the indication provided by meter 86 to be independent of the absolute magnitude of the signals applied to the amplifier 71, movements of the needle from the central position instead indicating variations in thickness of the material 9 which occur at too rapid a rate for the corresponding voltage variations to be eliminated by the network 91. The voltage of the point C is also applied to a variable tuned amplifier 97 comprising a twin-T input network, an amplifying valve 107 and a magic-eye indicator 111. By adjustment of the tuning of the twin-T network, periodic components in the voltage appearing at the points C may be selected by the amplifier and their existence indicated by the indicator 111. In addition, the voltage at the point D which likewise indicates variations in the thickness of the material 9, is applied to a modulating and integrating circuit 98 comprising a switching circuit in which diodes 114, 115 are switched by an input squarewave applied to transformer winding 121 to superimpose square-wave modulation upon the voltage at the point D. This is amplified by valve 125, rectified by diode 132 and smoothed by the input network to cathode follower 140, the output from which is applied to the meter 86 which for this purpose may be switched to the position shown in the drawing. The meter in this position consequently indicates the average amount of the deviation of the thickness of the material 9 from a mean value. In order to obtain a more accurate measure of this quantity the circuit shown in Fig. 10 may be connected between the points F, G. A time switch 148 closes the circuit between the points F, G for a predetermined length of time, say three minutes, to energize the motor 147 which runs at a speed proportional to the voltage applied thereto. A semi-circular disc 150 attached to the shaft of the motor 147 periodically interrupts a beam of light so that pulses are supplied from a photo-cell 153 through a relay 154 to a counter 155. At the end of the predetermined interval, the number of pulses counted by the counter 155 gives a measure of the mean value of the output of cathode follower 140. Measuring head.-The capacitor electrodes 4, 5, 6 and the male portion of the connector to the cable 2 are mounted on a base plate 10 which forms the front cover for a hollow casing 52 which is closed at the rear by a cover 53. Fig. 6 shows a rear view of the measuring head with the cover 53 removed. In order to equalize the capacitances between each of the outer electrodes 4, 6 and the central electrode 5, the wire 15 from the electrode 6 is extended at 57 to have the same length as the wire 17 from the electrode 4. Wires 15 and 17 are connected to terminals 22, 24 of the connector respectively; these terminals are separated by a screen from the terminal 23, this screen cooperating with a further screen within the female portion of the connector so that the voltages carried by the terminals 22, 24 are completely isolated from that carried by the terminal 23. Fig. 7 shows the inner view of the cover 53. An adjustable plug 55 extends through the cover 53 and by movement of this it is possible to adjust the position of the wire 57 to provide a rough adjustment for balancing the capacitances between the two lateral electrodes and the central electrode. Fine adjustment is provided by means of a metallic blade 58 which may be rotated by means of a knurled disc 59, this blade providing for variation of the capacitance between the terminal 23 and the terminals 22 and 24.